DOCSLIB.ORG

On Rate Constants: Simple Collision Theory, Arrhenius Behavior, and Activated Complex Theory

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
On Rate Constants: Simple Collision Theory, Arrhenius Behavior, and Activated Complex Theory On Rate Constants: Simple Collision Theory, Arrhenius Behavior, and Activated Complex Theory 17th February 2010 0.1 Introduction Up to now, we haven't said much regarding the rate constant k. It should be apparent from the discussions, however, that: • k is constant at a specific temperature, T and pressure, P • thus, k = k(T,P) (rate constant is temperature and pressure depen- dent) • bear in mind that the rate constant is independent of concentrations, as the reaction rate, or velocity itself is treated explicity to be concen- tration dependent In the following, we will consider how the physical, microscopic detaails of reactions can be reasoned to be embodied in the rate constant, k. 1 Simple Collision Theory Let's consider the following gas-phase elementary reaction: A + B ! Products The reaction rate is straightforwardly: 1 Rate = k[A]α[B]β = k[A]1[B]1 α = 1 β = 1 N N = k A B V = volume V V Recall previous discussions of the total collisional frequency for heteroge- neous reactions: 8kT ∗ ∗ ZAB = σAB nA nB s πµ ∗ NA ∗ NB where the nA = V ; nB = V are number of molecules/particles per unit volume. We can see the following: 8kT NA NB ZAB = σAB s πµ V V k Here we see that the concepts| of collisions{z } from simple kinetic theory can be fundamentally related to ideas of reactions, particularly when we consider that elementary reactions (only for which we can write rate expressions based on molecularity and order mapping) can be thought of proceeding due to collisions (or interactions of some sort) of monomers (unimolecular), dimers(bimolecular), trimers (trimolecular), etc. If we are to naively say that reactions occur due only to collisions of parti- cles (keep in mind the nature of the system { gas-phase,elementary reaction), then we can at the zero'th order equate the maximum reaction rate to the total collisional frequency for heterogeneous pairs: max R = ZAB max 1 1 8kT NA NB k [A] [B] = σAB s πµ V V k | {z } max 8kT k ≡ σAB s πµ 2 1.1 Simple Collision Theory: Caveats Simple collision theory (SCT), we see from above, remarkably predicts an expression for the microscopic rate constant that relates to the dimensions of the reactive species, their mass, and temperature. The form we determined above assumes two things: • All collisions are of sufficient energy that chemical transformation can occur • Steric/orientational nature of collision is always correct/accommodating Thus, we need to consider the effects of collision energy and collision sterics and/or orientation in our discussion of simple collision theory and its application to defining the reate constant, k. • For energetic considerations, we can empirically add a factor to ac- count for the probability of a collision having a sufficient energy, vis-a-vis, Emin, for collision. When we multiply the total collisional frequency by this probability, we can describe the fraction of collisions that will energetically be able to progress from reactants to products. The energy probability is take to be Boltzmann-like: −Emin P robability(Emin) / e RT 3 • For steric/orientational nature of collision, we introduce a steric factor (empirically), p • p < 1 generally Thus, we can write a more general expression for the collision theory based reaction rate as: −Emin Rate = ZAB p e RT E 8kT − min NA NB = p σAB e RT s πµ V V Thus we arrive at a corrected Simple collision theory expresion for the rate constant: 8kT −Emin RT kSCT = p σAB e s πµ 8kT Emin ln(kSCT ) = ln p σAB − " s πµ # RT Note the temperature dependence of the rate constant with SCT: 1 kSCT / T 2 . In general, we can write this expression for the rate constant as: m −Emin=RT kgeneral = c T e (1) 2 Arrhenius Temperature Dependence 1 In general, experiments do not suggest a T 2 temperature dependence of the rate constant. Moreover, experiments demonstrate for most reactions that 1 the temperature dependence of ln(k) is linear with T . Thus, Arrhenius pro- posed the following relation between temperature and the rate constant: −Eactivation kArr = A e RT (2) 4 Thus, E 1 ln(k ) = ln(A) − activation Arr R T (3) The energy is the activation energy (as discussed above) and the A value is a temperature-independent freqency factor, or pre-exponential factor. Plotting ln(k) versus T −1 will yield a straight line with slope −Eactivation equal to R and y intercept of ln(A). The pre-exponential factor in this case if independent of temperature, con- trasted with the SCT result from above. Though many reactions (across the spectrum of reaction orders, mechanisms, etc.) follow Arrhenius behavior, there are exceptions (as always). 3 Activated Complex Theory; Transition State The- ory In this section, we will consider a further refinement of our formulation of a reaction on the atomic level. Up to now, we have not entertained the possibility of short-lived, highly unstable intermediates appear- ing/being generated upon the initial "collision" of reactive species. Eyring and co-workers postulated the presence of these highly unstable, fleeting, transition states, and furthermore suggested an equilibrium between this transition state and the reactive species. The transition state is also consid- ered an activated complex, hence the nomenclature Activated Complex Theory (as well as Transition State Theory). A further important aspect of invoking the activated complex is that for a reaction such as AB + C ! A + BC, the path the reaction follows (if depicted on a three-dimensional potential energy surface) is the minimum energy path. That is, the reaction will not follow along a reaction coor- dinate that requires any higher energetic cost than is minimally necessary. See Figure 36.19 in Engell and Reid for a represenation of a representative 3-D potential energy surface. Assumptions of activated complex theory: • Equilibrium exists between reactants and activated complex 5 • Reaction coordinate can be mapped onto a single energetic degree of freedom of the activated complex (i.e., a vibrational degree of freedom corresponding to bond-stretching) The kinetic mechanism incorporating the activated complex is now: k1 A + B )−−−*− ABy k−1 ABy −k!2 P roducts The differential rate expression for A becomes: d[A] = 0 = −k [A][B] + k [ABy] dt −1 −1 y y k1 Kc [AB ] = [A][B] = o [A][B] k−1 c Note the dependence of the equilibrium constant on the standard state con- centration, co: y [AB ] y o o AB c Ky = c = c [A] [B] [A] [B] co co The rate of product, P, formation (equal to the reaction rate) is: d[P ] Rate = = k [ABy] dt 2 and since we know what [ABy] is from equilibrium of the reactants with the activated complex: d[P ] k Ky Rate = = 2 c [A][B] dt co Now, we will consider how to refine our understanding of k2. Consider: 6 • We have formulated our discussion with the assumption that there is a single reaction coordinate mapped onto a vibrational degree of freedom • Let this vibrational degree of freedom be a weak bond • Rate of product formation = Rate of reaction = Frequency of vibration of weak bond (inverse seconds) (Maximum rate since we are taking every initial motion along that vibration coordinate to lead to product formation) (k2 = ν). • If every κ of the vibrational cycles leads to product formation, then k2 = κν Thus, the reaction rate can be written as: d[P ] κ ν Ky Rate = = c [A][B] dt co Using elements of statistical mechanics (the details of which are outside the current scope, but are covered in: Moore and Pearson, Kinetics and Mechanism, John Wiley, 1981, pp. 159-186) κ k T Ky k = B c 2 h co where the h in the denominator is Planck's constant. Finally, if we recall that we can relate the equilibrium constant to the free energy change from reactant to activated complex, y − y ∆G = RT ln(Kc ) Thus, the rate constant becomes (taking κ = 1, which is a good approx- imation for most situations (exceptions include surface reactions)): k T y k = B e−∆G =RT 2 hco Since: 7 ∆Gy = ∆Hy − T ∆Sy we finally obtain the Eyring Equation: k T y y k = B e−∆H =RT e∆S =R 2 hco In the most general sense: k T y y k(T ) = B e−∆H =RT e∆S =R hco We see that activated complex theory allows us to incorporate free energy as a metric for determining the rate constant. In this sense, entropic factors come into play as well. In the next section, we will discuss the relation between the parameters of Arrhenius theory and ∆S y and ∆Hy. 4 Connection to Arrhenius Parameters The quantities ∆Hy and ∆Sy are now related to the Arrhenius pre-exponential factor and activation energy, Ea. Table 1. Relation Between Arrhenius and Eyring Parameters. Phase / Molecularity Activation Energy, Ea Pre-Exponential, A y e kB T ∆Sy=R Solution/Bimolecular Ea = ∆H + RT A = hco e y e kB T ∆Sy=R Solution/Unimolecular Ea = ∆H + RT A = h e y e kB T ∆Sy=R Gas/Unimolecular Ea = ∆H + RT A = h e 2 y e kB T ∆Sy=R Gas/Bimolecular Ea = ∆H + 2RT A = hco e 3 y e kB T ∆Sy=R Gas/Trimolecular Ea = ∆H + 3RT A = h(co)2 e 8.
Load more

Recommended publications
  • Chapter 9. Atomic Transport Properties
    NEA/NSC/R(2015)5 Chapter 9. Atomic transport properties M. Freyss CEA, DEN, DEC, Centre de Cadarache, France Abstract As presented in the first chapter of this book, atomic transport properties govern a large panel of nuclear fuel properties, from its microstructure after fabrication to its behaviour under irradiation: grain growth, oxidation, fission product release, gas bubble nucleation. The modelling of the atomic transport properties is therefore the key to understanding and predicting the material behaviour under irradiation or in storage conditions. In particular, it is noteworthy that many modelling techniques within the so-called multi-scale modelling scheme of materials make use of atomic transport data as input parameters: activation energies of diffusion, diffusion coefficients, diffusion mechanisms, all of which are then required to be known accurately. Modelling approaches that are readily used or which could be used to determine atomic transport properties of nuclear materials are reviewed here. They comprise, on the one hand, static atomistic calculations, in which the migration mechanism is fixed and the corresponding migration energy barrier is calculated, and, on the other hand, molecular dynamics calculations and kinetic Monte-Carlo simulations, for which the time evolution of the system is explicitly calculated. Introduction In nuclear materials, atomic transport properties can be a combination of radiation effects (atom collisions) and thermal effects (lattice vibrations), this latter being possibly enhanced by vacancies created by radiation damage in the crystal lattice (radiation enhanced-diffusion). Thermal diffusion usually occurs at high temperature (typically above 1 000 K in nuclear ceramics), which makes the transport processes difficult to model at lower temperatures because of the low probability to see the diffusion event occur in a reasonable simulation time.
    [Show full text]
  • SF Chemical Kinetics. Microscopic Theories of Chemical Reaction Kinetics
    SF Chemical Kinetics. Lecture 5. Microscopic theory of chemical reaction kinetics. Microscopic theories of chemical reaction kinetics. • A basic aim is to calculate the rate constant for a chemical reaction from first principles using fundamental physics. • Any microscopic level theory of chemical reaction kinetics must result in the derivation of an expression for the rate constant that is consistent with the empirical Arrhenius equation. • A microscopic model should furthermore provide a reasonable interpretation of the pre-exponential factor A and the activation energy EA in the Arrhenius equation. • We will examine two microscopic models for chemical reactions : – The collision theory. – The activated complex theory. • The main emphasis will be on gas phase bimolecular reactions since reactions in the gas phase are the most simple reaction types. 1 References for Microscopic Theory of Reaction Rates. • Effect of temperature on reaction rate. – Burrows et al Chemistry3, Section 8. 7, pp. 383-389. • Collision Theory/ Activated Complex Theory. – Burrows et al Chemistry3, Section 8.8, pp.390-395. – Atkins, de Paula, Physical Chemistry 9th edition, Chapter 22, Reaction Dynamics. Section. 22.1, pp.832-838. – Atkins, de Paula, Physical Chemistry 9th edition, Chapter 22, Section.22.4-22.5, pp. 843-850. Collision theory of bimolecular gas phase reactions. • We focus attention on gas phase reactions and assume that chemical reactivity is due to collisions between molecules. • The theoretical approach is based on the kinetic theory of gases. • Molecules are assumed to be hard structureless spheres. Hence the model neglects the discrete chemical structure of an individual molecule. This assumption is unrealistic. • We also assume that no interaction between molecules until contact.
    [Show full text]
  • Eyring Equation
    Search Buy/Sell Used Reactors Glass microreactors Hydrogenation Reactor Buy Or Sell Used Reactors Here. Save Time Microreactors made of glass and lab High performance reactor technology Safe And Money Through IPPE! systems for chemical synthesis scale-up. Worldwide supply www.IPPE.com www.mikroglas.com www.biazzi.com Reactors & Calorimeters Induction Heating Reacting Flow Simulation Steam Calculator For Process R&D Laboratories Check Out Induction Heating Software & Mechanisms for Excel steam table add-in for water Automated & Manual Solutions From A Trusted Source. Chemical, Combustion & Materials and steam properties www.helgroup.com myewoss.biz Processes www.chemgoodies.com www.reactiondesign.com Eyring Equation Peter Keusch, University of Regensburg German version "If the Lord Almighty had consulted me before embarking upon the Creation, I should have recommended something simpler." Alphonso X, the Wise of Spain (1223-1284) "Everything should be made as simple as possible, but not simpler." Albert Einstein Both the Arrhenius and the Eyring equation describe the temperature dependence of reaction rate. Strictly speaking, the Arrhenius equation can be applied only to the kinetics of gas reactions. The Eyring equation is also used in the study of solution reactions and mixed phase reactions - all places where the simple collision model is not very helpful. The Arrhenius equation is founded on the empirical observation that rates of reactions increase with temperature. The Eyring equation is a theoretical construct, based on transition state model. The bimolecular reaction is considered by 'transition state theory'. According to the transition state model, the reactants are getting over into an unsteady intermediate state on the reaction pathway.
    [Show full text]
  • Department of Chemistry
    07 Sept 2020 2020–2021 Module Outlines MSc Chemistry MSc Chemistry with Medicinal Chemistry Please note: This handbook contains outlines for the modules comprise the lecture courses for all the MSc Chemistry and Chemistry with Medicinal Chemistry courses. The outline is also posted on Moodle for each lecture module. If there are any updates to these published outlines, this will be posted on the Level 4 Moodle, showing the date, to indicate that there has been an update. PGT CLASS HEAD: Dr Stephen Sproules, Room A5-14 Phone (direct):0141-330-3719 email: [email protected] LEVEL 4 CLASS HEAD: Dr Linnea Soler, Room A4-36 Phone (direct):0141-330-5345 email: [email protected] COURSE SECRETARY: Mrs Susan Lumgair, Room A4-30 (Teaching Office) Phone: 0141-330-3243 email: [email protected] TEACHING ADMINISTRATOR: Ms Angela Woolton, Room A4-27 (near Teaching Office) Phone: 0141-330-7704 email: [email protected] Module Topics for Lecture Courses The Course Information Table below shows, for each of the courses (e.g. Organic, Inorganic, etc), the lecture modules and associated lecturer. Chemistry with Medicinal Chemistry students take modules marked # in place of modules marked ¶. Organic Organic Course Modules Lecturer Chem (o) o1 Pericyclic Reactions Dr Sutherland o2 Heterocyclic Systems Dr Boyer o3 Advanced Organic Synthesis Dr Prunet o4 Polymer Chemistry Dr Schmidt o5m Asymmetric Synthesis Prof Clark o6m Organic Materials Dr Draper Inorganic Inorganic Course Modules Lecturer Chem (i) i1 Metals in Medicine
    [Show full text]
  • (A) Reaction Rates (I) Following the Course of a Reaction Reactions Can Be Followed by Measuring Changes in Concentration, Mass and Volume of Reactants Or Products
    (a) Reaction rates (i) Following the course of a reaction Reactions can be followed by measuring changes in concentration, mass and volume of reactants or products. g Measuring a change in mass Measuring a change in volume Volume of gas produced of gas Volume Mass of beaker and contents of beaker Mass Time Time The rate is highest at the start of the reaction because the concentration of reactants is highest at this point. The steepness (gradient) of the plotted line indicates the rate of the reaction. We can also measure changes in product concentration using a pH meter for reactions involving acids or alkalis, or by taking small samples and analysing them by titration or spectrophotometry. Concentration reactant Time Calculating the average rate The average rate of a reaction, or stage in a reaction, can be calculated from initial and final quantities and the time interval. change in measured factor Average rate = change in time Units of rate The unit of rate is simply the unit in which the quantity of substance is measured divided by the unit of time used. Using the accepted notation, ‘divided by’ is represented by unit-1. For example, a change in volume measured in cm3 over a time measured in minutes would give a rate with the units cm3min-1. 0.05-0.00 Rate = 50-0 1 - 0.05 = 50 = 0.001moll-1s-1 Concentration moll Concentration 0.075-0.05 Rate = 100-50 0.025 = 50 = 0.0005moll-1s-1 The rate of a reaction, or stage in a reaction, is proportional to the reciprocal of the time taken.
    [Show full text]
  • Kinetics 651
    Chapter 12 | Kinetics 651 Chapter 12 Kinetics Figure 12.1 An agama lizard basks in the sun. As its body warms, the chemical reactions of its metabolism speed up. Chapter Outline 12.1 Chemical Reaction Rates 12.2 Factors Affecting Reaction Rates 12.3 Rate Laws 12.4 Integrated Rate Laws 12.5 Collision Theory 12.6 Reaction Mechanisms 12.7 Catalysis Introduction The lizard in the photograph is not simply enjoying the sunshine or working on its tan. The heat from the sun’s rays is critical to the lizard’s survival. A warm lizard can move faster than a cold one because the chemical reactions that allow its muscles to move occur more rapidly at higher temperatures. In the absence of warmth, the lizard is an easy meal for predators. From baking a cake to determining the useful lifespan of a bridge, rates of chemical reactions play important roles in our understanding of processes that involve chemical changes. When planning to run a chemical reaction, we should ask at least two questions. The first is: “Will the reaction produce the desired products in useful quantities?” The second question is: “How rapidly will the reaction occur?” A reaction that takes 50 years to produce a product is about as useful as one that never gives a product at all. A third question is often asked when investigating reactions in greater detail: “What specific molecular-level processes take place as the reaction occurs?” Knowing the answer to this question is of practical importance when the yield or rate of a reaction needs to be controlled.
    [Show full text]
  • Spring 2013 Lecture 13-14
    CHM333 LECTURE 13 – 14: 2/13 – 15/13 SPRING 2013 Professor Christine Hrycyna INTRODUCTION TO ENZYMES • Enzymes are usually proteins (some RNA) • In general, names end with suffix “ase” • Enzymes are catalysts – increase the rate of a reaction – not consumed by the reaction – act repeatedly to increase the rate of reactions – Enzymes are often very “specific” – promote only 1 particular reaction – Reactants also called “substrates” of enzyme catalyst rate enhancement non-enzymatic (Pd) 102-104 fold enzymatic up to 1020 fold • How much is 1020 fold? catalyst time for reaction yes 1 second no 3 x 1012 years • 3 x 1012 years is 500 times the age of the earth! Carbonic Anhydrase Tissues ! + CO2 +H2O HCO3− +H "Lungs and Kidney 107 rate enhancement Facilitates the transfer of carbon dioxide from tissues to blood and from blood to alveolar air Many enzyme names end in –ase 89 CHM333 LECTURE 13 – 14: 2/13 – 15/13 SPRING 2013 Professor Christine Hrycyna Why Enzymes? • Accelerate and control the rates of vitally important biochemical reactions • Greater reaction specificity • Milder reaction conditions • Capacity for regulation • Enzymes are the agents of metabolic function. • Metabolites have many potential pathways • Enzymes make the desired one most favorable • Enzymes are necessary for life to exist – otherwise reactions would occur too slowly for a metabolizing organis • Enzymes DO NOT change the equilibrium constant of a reaction (accelerates the rates of the forward and reverse reactions equally) • Enzymes DO NOT alter the standard free energy change, (ΔG°) of a reaction 1. ΔG° = amount of energy consumed or liberated in the reaction 2.
    [Show full text]
  • Predictive Models for Kinetic Parameters of Cycloaddition
    Predictive Models for Kinetic Parameters of Cycloaddition Reactions Marta Glavatskikh, Timur Madzhidov, Dragos Horvath, Ramil Nugmanov, Timur Gimadiev, Daria Malakhova, Gilles Marcou, Alexandre Varnek To cite this version: Marta Glavatskikh, Timur Madzhidov, Dragos Horvath, Ramil Nugmanov, Timur Gimadiev, et al.. Predictive Models for Kinetic Parameters of Cycloaddition Reactions. Molecular Informatics, Wiley- VCH, 2018, 38 (1-2), pp.1800077. 10.1002/minf.201800077. hal-02346844 HAL Id: hal-02346844 https://hal.archives-ouvertes.fr/hal-02346844 Submitted on 5 Feb 2021 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. 0DQXVFULSW &OLFNKHUHWRGRZQORDG0DQXVFULSW&$UHYLVLRQGRF[ Predictive models for kinetic parameters of cycloaddition reactions Marta Glavatskikh[a,b], Timur Madzhidov[b], Dragos Horvath[a], Ramil Nugmanov[b], Timur Gimadiev[a,b], Daria Malakhova[b], Gilles Marcou[a] and Alexandre Varnek*[a] [a] Laboratoire de Chémoinformatique, UMR 7140 CNRS, Université de Strasbourg, 1, rue Blaise Pascal, 67000 Strasbourg, France; [b] Laboratory of Chemoinformatics and Molecular Modeling, Butlerov Institute of Chemistry, Kazan Federal University, Kremlyovskaya str. 18, Kazan, Russia Abstract This paper reports SVR (Support Vector Regression) and GTM (Generative Topographic Mapping) modeling of three kinetic properties of cycloaddition reactions: rate constant (logk), activation energy (Ea) and pre-exponential factor (logA).
    [Show full text]
  • Wigner's Dynamical Transition State Theory in Phase Space
    Wigner’s Dynamical Transition State Theory in Phase Space: Classical and Quantum Holger Waalkens1,2, Roman Schubert1, and Stephen Wiggins1 October 15, 2018 1 School of Mathematics, University of Bristol, University Walk, Bristol BS8 1TW, UK 2 Department of Mathematics, University of Groningen, Nijenborgh 9, 9747 AG Groningen, The Netherlands E-mail: [email protected], [email protected], [email protected] Abstract We develop Wigner’s approach to a dynamical transition state theory in phase space in both the classical and quantum mechanical settings. The key to our de- velopment is the construction of a normal form for describing the dynamics in the neighborhood of a specific type of saddle point that governs the evolution from re- actants to products in high dimensional systems. In the classical case this is the standard Poincar´e-Birkhoff normal form. In the quantum case we develop a normal form based on the Weyl calculus and an explicit algorithm for computing this quan- tum normal form. The classical normal form allows us to discover and compute the phase space structures that govern classical reaction dynamics. From this knowledge we are able to provide a direct construction of an energy dependent dividing sur- face in phase space having the properties that trajectories do not locally “re-cross” the surface and the directional flux across the surface is minimal. Using this, we are able to give a formula for the directional flux through the dividing surface that goes beyond the harmonic approximation. We relate this construction to the flux- flux autocorrelation function which is a standard ingredient in the expression for the reaction rate in the chemistry community.
    [Show full text]
  • CHEMICAL KINETICS Pt 2 Reaction Mechanisms Reaction Mechanism
    Reaction Mechanism (continued) CHEMICAL The reaction KINETICS 2 C H O +→5O + 6CO 4H O Pt 2 3 4 3 2 2 2 • has many steps in the reaction mechanism. Objectives ! Be able to describe the collision and Reaction Mechanisms transition-state theories • Even though a balanced chemical equation ! Be able to use the Arrhenius theory to may give the ultimate result of a reaction, determine the activation energy for a reaction and to predict rate constants what actually happens in the reaction may take place in several steps. ! Be able to relate the molecularity of the reaction and the reaction rate and • This “pathway” the reaction takes is referred to describle the concept of the “rate- as the reaction mechanism. determining” step • The individual steps in the larger overall reaction are referred to as elementary ! Be able to describe the role of a catalyst and homogeneous, heterogeneous and reactions. enzyme catalysis Reaction Mechanisms Often Used Terms •Intermediate: formed in one step and used up in a subsequent step and so is never seen as a product. The series of steps by which a chemical reaction occurs. •Molecularity: the number of species that must collide to produce the reaction indicated by that A chemical equation does not tell us how step. reactants become products - it is a summary of the overall process. •Elementary Step: A reaction whose rate law can be written from its molecularity. •uni, bi and termolecular 1 Elementary Reactions Elementary Reactions • Consider the reaction of nitrogen dioxide with • Each step is a singular molecular event carbon monoxide.
    [Show full text]
  • CHEMISTRY.Pdf
    SYLLABUS FOR THE POST OF LECTURER 10+2 CHEMISTRY PHYSICAL CHEMISTRY Thermodynamics Partial molar properties; partial molar free energy, partial molar volume from density measurements, Gibbs- Duhem equation, Fugacity of gases, calculation of fugacity from P, T data concept of ideal solutions, Rault’s Law, Duhen-Margules equation, Henry Law, Concept of activity and activity co-efficients. Chemical Kinetics and Photochemistry Theories of reaction rates, absolute reaction rates and collision theory, ionic reactions, photochemical reactions, explosion reactions, flash photolysis. Surface Chemistry Langmuir adsorption isotherm, B.E.T. adsorption isotherm, Chemisorptions-its kinetics and thermodynamics. Electro Chemistry Liquid junction potential Quantum Chemistry Eigen functions and eigen values; Angular momentum and eigen values of angular momentum, spin, Pauli exclusion principle, operator concept and wave mechanics of simple systems, particle in ring and rigid rotator, simple harmonic oscillator and the Hydrogen atom. Postulates of quantum, mechanics, elementary concept of perturbation theory, application of variation method and perturbation method to simple harmonic oscillator. Schrödinger’s equation (time dependent). INORGANIC CHEMISTRY Description of VB, MO and VSEPR theories, Three electron bond, Hydrogen bond, theories of hydrogen bonding, Inorganic semi conductors and super conductors, structure and bonding in Zoolites and orthosilicates, Borates; Nitrogen-Phosphorus cyclic compounds polyhalides. Organometallic Compounds Definition, classification, Transition metal-to carbon sigma bonded compounds. Synthesis and bonding of Alkyne and allyl transition metal complexes, cyclo pentadienyl and arene metal complexes, Homogeneous catalysis involving organometallic compounds; Hydrogenation, Polymerisation, preparation, structure and applications of organometallic compounds of Boron. Coordination Numbers Spectrochemical series, John-Teller distortion, colour and magnetic properties of coordination compounds, crystal field theory, M.O treatment of actahedral complexes.
    [Show full text]
  • Lecture 17 Transition State Theory Reactions in Solution
    Lecture 17 Transition State Theory Reactions in solution kd k1 A + B = AB → PK = kd/kd’ kd’ d[AB]/dt = kd[A][B] – kd’[AB] – k1[AB] [AB] = kd[A][B]/k1+kd’ d[P]/dt = k1[AB] = k2[A][B] k2 = k1kd/(k1+kd’) k2 is the effective bimolecular rate constant kd’<<k1, k2 = k1kd/k1 = kd diffusion controlled k1<<kd’, k2 = k1kd/kd’ = Kk1 activation controlled Other names: Activated complex theory and Absolute rate theory Drawbacks of collision theory: Difficult to calculate the steric factor from molecular geometry for complex molecules. The theory is applicable essentially to gaseous reactions Consider A + B → P or A + BC = AB + C k2 A + B = [AB] ╪ → P A and B form an activated complex and are in equilibrium with it. The reactions proceed through an activated or transition state which has energy higher than the reactions or the products. Activated complex Transition state • Reactants Has someone seen the Potential energy transition state? Products Reaction coordinate The rate depends on two factors, (i). Concentration of [AB] (ii). The rate at which activated complex is decomposed. ∴ Rate of reaction = [AB╪] x frequency of decomposition of AB╪ ╪ ╪ K eq = [AB ] / [A] [B] ╪ ╪ [AB ] = K eq [A] [B] The activated complex is an aggregate of atoms and assumed to be an ordinary molecule. It breaks up into products on a special vibration, along which it is unstable. The frequency of such a vibration is equal to the rate at which activated complex decompose. -d[A]/dt = -d[B]/dt = k2[A][B] Rate of reaction = [AB╪] υ ╪ = K eq υ [A] [B] Activated complex is an unstable species and is held together by loose bonds.
    [Show full text]